The invention relates to a centrifugal pump for delivering hot fluids, having a contacting shaft seal, a seal housing for the shaft seal, and a return line for a partial flow of the delivered fluid.
A centrifugal pump of this kind is described in U.S. Pat. No. 5,795,129 (=DE 42 30 715), which is used as a feed pump for delivering hot fluids. A delivered fluid emerging from the relief device thereof forms a partial flow of the delivered fluid. This partial flow, also known as “relief water”, is used to cool a mechanical seal. For this purpose, it flows completely through the seal chamber thereof and, in doing so, dissipates the frictional heat which arises during the operation of the mechanical seal. After this, the relief water is discharged from the seal chamber via a return line, which connects the seal housing to a pump stage. This type of shaft seal cooling can be used only up to a certain operating temperature of the delivered fluid.
A centrifugal pump having a sealing system for relatively high operating temperatures is described in European patent application no. EP 588,259 (=DE 195.18 564). Disposed between a seal chamber containing a mechanical seal and the interior of the pump is another sealing element, which rests against the rotating part of the pump. This sealing element is composed of a high-polymer plastic. To reduce heat input, the relief water in this design is not passed through the seal chamber. To achieve this, the sealing element shields the seal chamber from the hot delivered fluid in the interior of the pump and, at the same time, ensures pressure compensation relative to the seal chamber. The relief water is returned to the suction side of the centrifugal pump by a return line. The seal housing is integrated into a cooling circuit, the cooling fluid of which has initially been taken from the delivered fluid. Heat is removed from the cooling fluid by a separate cooling circuit connected to the seal housing. For this purpose, conventional external cooling systems can be employed.